The German patent DE 198 41 842 C2 discloses a powder clearcoat slurry which is free from organic solvents and external emulsifiers and comprises solid spherical particles with an average size of from 0.8 to 20 μm and a maximum size of 30 μm, said slurry having an ion-forming group content of from 0.05 to 1 meq/g, a neutralizing agent content of from 0.05 to 1 meq/g, and a viscosity of    (i) from 50 to 1 000 mPas at a shear rate of 1 000 s−1,    (ii) from 150 to 8 000 mPas at a shear rate of 10 s−1,    (iii) from 180 to 12 000 mPas at a shear rate of 1 s−1.The binder used is a methacrylate copolymer having an OH number of 110 mg KOH/g (cf. Preparation Example 1 on page 6 lines 30 to 47 of the patent). The powder clearcoat slurry of Example 1 of the patent (cf. page 7 lines 31 to 54 of the patent), prepared using this binder, has a carboxyl group content of 0.52 meq/g of solids and a carboxylate group content of 0.22 meq/g of solids, from which the degree of neutralization is calculated as 42%. The particle size is 6 μm. The powder clearcoat slurry of Example 2 of the patent (cf. page 7 line 56 to page 8 line 22 of the patent), prepared using the binder, has a carboxyl group content of 0.19 meq/g of solids and a carboxylate group content of 0.10 meq/g of solids, giving a degree of neutralization of 52%.
The known powder clearcoat slurry is prepared by    1) emulsifying an organic solution comprising binder and crosslinker to give an emulsion of the oil-in-water type,    2) removing the organic solvent or the organic solvents, and    3) replacing by water some or all of the volume of solvent removed, to give a powder clearcoat slurry comprising solid spherical particles,where    4) additionally, at least one ionic, especially anionic, thickener and at least one nonionic associative thickener are added to the powder clearcoat slurry.
This powder clearcoat slurry can be prepared with a small number of processing steps; on the basis of its typical powder slurry properties, with residual solvent contents of <1%, and its particle sizes, it exhibits advantageous application characteristics. Even without the assistance of organic solvents, there is generally no popping at the required film thicknesses of approximately 40–50 μm. Moreover, the particles of the slurry, owing to mixing of their constituents in solution, are very homogeneous.
However, the clearcoats produced from the slurry do exhibit blushing when exposed to moisture. Furthermore, they do not achieve the required chemical resistance of clearcoats produced from customary and known, commercial two-component clearcoat materials.
Attempts to eliminate these disadvantages by raising the crosslinking density of the clearcoats are accompanied by new problems. The corresponding powder clearcoat slurries no longer dry in powder form, and at relatively high coat thicknesses, after curing, show film defects in the form of popping marks and stress cracks.